This is a single-center, randomized, open-label, dose-ranging, phase I comparative trial of intradermal (ID) and intramuscular (IM) injection with subvirion inactivated influenza A/H5N1 vaccine in healthy adults, 18 to 40 years old, inclusive. This study is designed to investigate the safety, reactogenicity, and dose-related immunogenicity of an investigational inactivated influenza A/H5N1 virus vaccine given by ID injection compared to IM injection. The primary objectives of this study are to: compare dose-related safety and reactogenicity profiles of ID and IM injection with subvirion inactivated influenza A/H5N1 vaccine among healthy young adults; compare the dose-related immunogenicity of subvirion inactivated influenza A/H5N1 vaccine given by ID with vaccine given by IM injection among healthy young adults 1 month after receipt of the second dose of vaccine; and provide information for the selection of the best dose levels for further studies. The secondary objectives of this study are to: evaluate dose-related immunogenicity and the percent of subjects responding approximately 1 and 7 months after the first vaccination; and evaluate the dose-related safety, reactogenicity and immunogenicity following receipt of a third dose of vaccine administered 6-7 months after the second dose of vaccine. The study will have 2 comparison arms (IM and ID), and 2 dosage levels will be evaluated in each arm (4 vaccine groups total). Subjects will be randomized 1:1:1:1 (25 subjects in each group) to receive 2 doses 1 month apart of an inactivated influenza A/H5N1 vaccine containing 15 mcg or 45 mcg of H5 HA by the IM route; or one-fifth of the IM dose (3 mcg or 9 mcg) by the ID route. Subjects will maintain a memory aid recording oral temperature, and systemic and local adverse events for 7 days after each inoculation. Serum for immunogenicity evaluations will be obtained prior to first vaccination, at Day 0, prior to second vaccination, at Day 28, and on Day 56 and approximately Day 215 (7 months) after dose 1. This study is linked to DMID protocol 07-0022.